Major cleanup of new Routing, Module, and Controller system.

Global/Functions.php
* Should not exit() if response code is unknown

Global/Http/*, Global/Template/Http/*
* Allows you to throw special `Exception`s and return `ErrorResponse`s to cleanly exit after an error condition has occurred.  NOTE: Most possible HTTP errors have not been implemented.  Also, we may make "client errors" (4xx) unthrowable since these are not actually errors or exceptions on the server side and can actually be tested for in an appropriate way.

Global/Module.php
* Reverting back to giving Module its own execute() function.  This can be overridden if your module is very simple, but please consider using proper Controllers before you just go overriding execute().

ModuleController.php renamed to PhpwebsiteController.php
* Singleton functionality removed from ModuleController/PhpwebsiteController and put into ModuleRepository.
* ModuleRepository is the place to go for information about installed Modules.
* This change was made because there is no particular reason to have only one instance of PhpwebsiteController, and I see this as the potential means of making "sub-requests" in the future.  Additionally, it could be instantiated by other php software (like a certain sysadmin's scripts) and operated upon just like any other object.  Could also be useful for operating on multiple sites at a time, ie $site1 = new PhpwebsiteController(dbinfo); $site2 = new PhpwebsiteController(otherdbinfo).  That sort of functionality is definitely not available as things stand now but I think it will become important soon.

* Removed URI parsing and routing from Request object since this is not the Request object's responsibility - something else uses the data in there to determine how to route the request.  However, since it's pretty obvious that it would be nice to be able to slice-and-dice the URL in Request to give modules the flexibility to completely define their own routing behavior, Request has a function getSubRequest(), which will return a new Request with a portion of the URL removed.
Further changes to how you can split up the URL in Request